A nanometer-scale magnet, sometimes referred to as a nanomagnet, has a magnetization direction that can align along any of several magnetic axes in the nanomagnet. A nanomagnet can be created that has an easy axis, which is a relatively stable axis, and a hard axis, which is a less stable axis. A magnetization direction alignment in one direction along the easy axis of a nanomagnet can represent a first value, such as a zero, and a magnetization direction alignment in the other direction along the easy axis can represent a second value, such as a one. There has been success in propagating a signal along a series of nanomagnets.
In one technique, a force is applied to a series of nanomagnets to cause the magnetization direction of each nanomagnet to align along the hard axis of the nanomagnet. The force is removed, and the magnetization direction of a first nanomagnet in the series of nanomagnets is perturbed to cause the magnetization direction of the first nanomagnet to align in a particular direction along the easy axis of the nanomagnet. Magnetic dipole field coupling between adjacent nanomagnets ideally causes a cascade of magnetization direction easy axis alignments across the series of nanomagnets. Thus, assuming a reliable cascade of magnetization direction alignments along the series of nanomagnets, a signal can be propagated across the series of nanomagnets.
Methods and apparatus for creating nanomagnetic logic circuits which enable logic operations to be implemented entirely in the magnetic domain are disclosed in U.S. patent application Ser. No. 12/131,669 entitled NANOMAGNETIC SIGNAL PROPAGATION AND LOGIC GATES, filed Jun. 2, 2008, which is hereby incorporated by reference herein in its entirety. In order to use an output of one nanomagnetic logic circuit as an input to a subsequent nanomagnetic logic circuit in a clocked sequential system, the output must be stored in some manner between clock cycles. Merely designating one of the signal propagating nanomagnets at the end of a logic circuit as a register nanomagnet is problematic because the force that is applied to the nanomagnetic logic circuits to force the nanomagnets into hard axis alignment would also destroy the output signal (i.e., magnetization direction) of the register nanomagnet. One alternative is to convert the output signal from the magnetic domain to the electronic domain at the end of a clock cycle, and convert the output signal back from the electronic domain to the magnetic domain at the beginning of the next clock cycle. However, energy conversions require additional power and add delay that is inherent in such processes. Therefore, there is a need for a mechanism for storing the output of a nanomagnetic logic circuit in the magnetic domain.